Magnetic snap action switch



T. N. FLIGHT ET AL MAGNETIC SNAP ACTION SWITCH April 24, 1951 Filed July 17, 1948 024 WM ,4 5, mm iwm hive/Mora a! "2,209 Af/or eys Patented Apr. 214, 1951 em OFFICE MAGNETIC SNAP ACTION SWITCH Theodore N. Flight, Slough, William H. Wilson, Camberley, and Arthur John Chinn, Slough, England, assignors to The Rheostatic Company Limited, Slough, England, a British company Application July 17, 1948, Serial No. 39,276

In Great Britain July 26, 1947 4 Claims. (01. 200-67) This invention relates to magnetic snap action switches, for use on alternating current circuits, of the micro-gap type inwhich contacts of relatively large mass and of a metal having good heat conductivity are associated with an armature, a springlever and a permanent magnet, the moving contact being arranged to have a movement of separation from the fixed contact limited to an amount suflicient only to prevent the re-strikingof an are at the voltage of the circuit broken and at such a speed as to reach this distance within the time of half a cycle.

In the usual type of such switches with a single armature the load on the end of the spring switchlever is equal to the total magnetic force or pull on the armature. Ihis load is usually far in access of that necessaryto assure adequate contact pressure and due to" the physical characteristics of the materials used in, and the smallness of the parts of, such switches, the aforementioned load on the switch-lever is inconvenient to provide for.

This invention contemplates a switch in which the load on the switch lever is reduced to a value more nearly equal to the relatively small load required to assure adequate contact pressure.

In the preferred form of the invention a resilient switch lever carries a double armature structure so disposed in relation to the magnet that the load borne by the resilient lever is only the difierence in the magnetic pull on the twoarmatures. It is then provided that the magnetic pull on one armature is in all positions of the switch greater than on the second armature, resulting froman adjustable magnetic bias which can be arranged to act in a specific direction relative to the switch contacts, 1. e. bias either to the open or to the closed switch position.

Thus, when the armature structure comprises two similar armature elements mechanically connected together, and mounted one on each side of a magnet, the magnet will exert a force on the armature structure in one direction and also a.

tained nearer to the magnet than the other arma ture in all positions of the switch lever arm, so that the force on the former armature will always be larger than that on th latter armature.

In an alternative form of the invention, one of the armatures has a magnetic permeability higher than the other. Since the force on each armature is proportional to the permeability of the material from which the armature is fashioned, a greater force will be exerted'on the higher-permeability armature. The permeabilities can base arranged that a greater force is exerted on the higher permeability armature in all positions of the lever arm.

To provide for the proper magnitude of pressure between the contacts at themoment the contacts make, a relatively high force change is necessary. This force change is caused by movement of the armatures and in a switch constructed in accordance-with this invention, is equal to the sum of the force changes on the two armatures. Thus, if the armature approaching the magnet experiences an increase in force of 30 dynes, and the armature receding from the magnet experiences a reduction in forceof 30 dynes, thepressure between the contacts atthe moment of make Will be proportional to the total force change, 60 dynes.

In switches according tothepreferred form of this invention the lever carrying one contact of the switch and the twin armature unit is a resilient member rigidly supported from the switch base and receiving movement from an actuator such as a thermal member of a thermostat, the moving portion of a pressure sensitive element or any other actuating device. The gradual movement of the actuator is stored in the resilient lever as a force tending to separate the switch contacts and when this force exceeds the set pressure difference existing between the magnet and the two armatures the switch contacts separate with a snap action.

The invention is illustrated in the accompanying drawings in which Figure 1 represents a perspective view of one embodiment of the improved switch of the invention, and Figure 2 is a View of the improved switch using a high coercivity magnet of short rectangular form.

In the construction shown in Figure 1 a twin armature unit consisting of two armatures II, I! rigidly attached to each other and to the end of the resilient lever l3 embraces the poles of the magnet I4. With actuator 16 withdrawn'from contact with the resilient tongue I3 the pressure between contacts H, H! is proportional to theadjusted difference in the pull of the magnet on armatures H, [2. The pressure and movement of the actuator |B- against theresilient tongue l3 generates a force in tongue l3 in opposition to the .resultant magnetic pull between the twin armature unit H, I2 and the magnet, and when the movement of actuator l6 has generated sufficient force to overcome this pull the switch opens to the aforementioned limited amount with a snap .action. It. will be seen that in a switch according to this invention the total load to be borne by :the resilient switch lever H3 at the moment of switch opening is merely the adjusted out-of-balance attraction existing between the two armatures H and I2 and the magnet Id.

In Figure 2 all of the parts are similar to those in Fig. l and have similar reference numerals with the exception of the magnet 20 which is in this figure shown as a short rectangular magnet which is rigidly attached to the base by clamping means (not shown) and is completely embraced on two sides by the twin armature unit. This construction so increases the magnetic efficiency of the armature magnet assembly that it ispossibletoobtain the required pressure between such: contacts with magnets of high coercive ma terial weighing only a fractionof. what has been previously found necessary.-

Inco-pending application Serial No. 718,636, filed December 2.7, 1946, now Patent-No. 2,518,966, August 15, 1950, there.- is disclosed and claimed a magnetic snap action switch which is constructed inaccordanoe withthese principles but which employs a non-resilient armatureecarrying lever actuated-by a; resilient member. In a second. co-

pending applicationserial No. 64,326, filed De-- cernber9, 1948, now Patent Nos 2,519,558, August 22, 1950, thereisdisolosed and. claimed athermostatically controlled device. employing a switch constructed in accordance with the disclosure herein" We-claim:

1. A magnetic snap action switch comprising a magnet, a movable resilientlever arm, a pair of armature'members carried bysaid resilient lever arm for movement therewith and disposed on opposite sides. of said magnet, a pair of-switch contacts, one of which switch contacts is actuated by saidresilient lever arm, the second contact being fixed in position relative to said first contact and adapted to cooperate therewith, and means for limitin the movement of the resilient lever arm in switch-opening. direction, the relative magnetic properties of the armature members and their. relative. distances from the magnet being such that the resilient lever arm is biased in one direction in all of its positions.

2. A magnetic snap action switch as defined in claim 1 in which one of said armature members is positioned nearer to said magnet in all positions of the resilient lever arm than the other of said armature. members and the relative magnetic properties of said armature members are sucn that the resilient lever arm is always biased in a direction tending to move the armature member nearer the magnet toward the magnet.

3. A magnetic snap action switch as defined in claim 1 in which one of said armature members has a greater permeability than the other, and

the relative distances of the armature members 1 from the magnet are such that the resilient lever arm is always biased in a direction tending to move the higher permeability armature member toward the magnet.

4. A magnetic snap action switch comprising a movable resilient lever arm pivoted at one end and having a contact fixed thereto adjacent its other end, apair of armature members mounted on. said'rcsilient lever arm and extending substantially parallel thereto, a magnet fixedly mounted relative to said resilient lever arm and positioned between said armature members, a second contact fixedin position relative to said resilient lever arm such that one of said armature members is nearer to the magnet than the other in switch-closed position, and means for so limiting the movement of the resilient lever arm in switch-opening direction that the one of said' armature members which is the nearer to the magnet in switch-closed position remains the nearer to the magnet in all other positions of the resilient lever arm, whereby the resilient lever arm is' biased in the same direction in all of its positions.

THEODORE N. FLIGHT. WILLIAM H. WILSON. ARTHUR JOHN CHINN.

CES CITED following references are of record in the file of this patent:

UNITED STATES PATENTS 

